I'm getting ready to insulate the loft with 300mm glass fiber. I have 9 recessed spots installed (these ones) in the upstairs landing. They are 4W spots nearly flush with the ceiling when viewed from the loft. Covers I see for spots in the loft are very bulky (here, 25 x 23.6 x 18 cm and here, 19 x 19 x 14 cm). Will installing these covers impact insulation much? I'm sure thinning it out that much will hammer it but to what extent? And given these covers are rated for ~50W, more than ten-times the output, could I get away with making something smaller?